This invention deals generally with joint seals for concrete structures and more particularly with seals between precast concrete box modules used to form underground enclosures to store water.
The law in most jurisdictions requires control of the rate of discharge and the volume of storm water run-off from certain sites, but traffic safety requirements conflict with such controlled rates of discharge because they require accelerated surface drainage of storm water. A favorable solution to these conflicting requirements is an on-site underground storage structure used for retention or detention of storm water. Such a structure provides temporary storage of the storm water and controls its release from the structure at a predetermined rate dictated by the legal requirements or site conditions.
However, in addition to the control of rate of discharge, certain sites are not at all suitable for infiltration and recharge of the groundwater table. Some soil conditions are susceptible to sinkhole formation, and substrate pollution conditions may prohibit infiltration and require long term watertight water storage. Other site conditions may also require a watertight structure.
Precast box structures forming a horizontal tunnel structure from segments constructed off-site and assembled at the project site can be used for both short and long term storage. However, the watertight joints required in such a configuration are a challenge for the installer to make watertight. Post-tensioning the segments and squeezing rubber strips between adjacent concrete segments of the joints does not satisfy the goals of water tightness because of imperfections in the precast joint surface and the rubber strips. Furthermore, the inherent creep and relaxation properties of the joint rubber or other sealants used undermine the long-term water tightness. The change in dimensions from such creep and relaxation causes cracks and leaks at the joint.
It would be very beneficial to have available a transitional joint that provides short and long term stability for a watertight seal between precast concrete modules used underground.